With many mechanical devices, the displacement and the speed of a movable member have been detected minutely as information for performing feedback control or the like in recent years. For example, with a lens barrel of an auto focus camera, a focus cam mechanism is provided internally which converts the rotational drive force of an electric motor or the like into a linear drive force, so as to shift the focusing lens. In Japanese Laid-Open Patent Publication No. 2000-205808, there is disclosed a displacement detection device which detects the rotational displacement of a rotating tube included in such a focusing cam mechanism which is provided to this type of lens barrel.
This related art device comprises a magnetic pattern which is disposed upon the exterior peripheral surface of the lens barrel along its circumferential direction, and a magnetoresistive sensor (MR sensor) which is made to contact with the magnetic pattern in order to detect the rotational position of the movable barrel. The MR sensor is supported in a holder, and is biased or pressed via the holder towards the magnetic pattern by the spring force of a pressure spring. It is arranged that the MR sensor is capable of swinging with respect to the pressure spring.
However, with this type of related art device, since it is necessary for the holder to be held by the pressure spring with a certain degree of freedom, accordingly there is a problem of deterioration of detection accuracy being caused due to the occurrence of play between the pressure spring and the holder.